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Atomic force microscopy is an extremely versatile technique, featuring atomic-scale imaging resolution, and also offering the possibility to probe interaction forces down to few pN. Recently, this technique has been specialized to study the interaction between single living cells, one on the substrate, and a second being adhered on the cantilever. Cell–cell force spectroscopy offers a unique tool to investigate in fine detail intra-cellular interactions, and it holds great promise to elucidate elusive phenomena in physiology and pathology. Here we present a systematic study of the effect of the main measurement parameters on cell–cell curves, showing the importance of controlling the experimental conditions. Moreover, a simple theoretical interpretation is proposed, based on the number of contacts formed between the two interacting cells. The results show that single cell–cell force spectroscopy experiments carry a wealth of information that can be exploited to understand the inner dynamics of the interaction of living cells at the molecular level.

Antimicrobial peptides (AMPs) and lipopeptides (LPs) represent very promising molecules to fight resistant bacterial infections due to their broad-spectrum of activity, their first target, i.e. the bacterial membrane, and the rapid bactericidal action. For both types of molecules, the action mechanism starts from the membrane of the pathogen agents, producing a disorganization of their phase structure or the formation of pores of different size altering their permeability. This mechanism of action is based on physical interactions more than on a lock-and-key recognition event and it is difficult for the pathogens to rapidly develop an effective resistance. Very small differences in the sequence of both AMPs and LPs might lead to very different effects on the target membrane. Therefore, a correct understanding of their mechanism of action is required with the aim of developing new synthetic peptides, analogues of the natural ones, with specific and more powerful bactericidal activity. Atomic force microscopy (AFM), with its high resolution and the associated force spectroscopy resource, provides a valuable technique to investigate the reorganization of lipid bilayers exposed to antimicrobial or lipopeptides. Here, we present AFM results obtained by ours and other groups on the action of AMPs and LPs on supported lipid bilayers (SLBs) of different composition. We also consider data obtained by fluorescence microscopy to compare the AFM data with another technique which can be used on different lipid bilayer model systems such as SLBs and giant unilamellar vesicles. The outcomes here presented highlight the powerful of AFM-based techniques in detecting nanoscale peptide-membrane interactions and strengthen their use as an exceptional complementary tool to in vivo investigations. Indeed, the combination of these approaches can help decipher the mechanisms of action of different antimicrobials and lipopeptides at both the micro and nanoscale levels, and to design new and more efficient antimicrobial compounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strontium fluoride forms weakly-interacting interfaces with Ag(1 1 1). • Almost ideal and continuous dielectric layer is formed when growth is carried out at room temperature. • A valence band offset of 6.7 eV between Ag and SrF 2 is obtained for 5 nm of dielectric film. • High temperature growth causes the formation of 3D fluoride structures. Molecular beam epitaxy (MBE) is used to grow ultrathin SrF 2 layers at different temperatures on Ag(1 1 1) epitaxial films prepared on mica. The electronic properties, structure and morphology of the films are probed by ultraviolet and x-ray photoelectron spectroscopies (UPS and XPS) supported by ab-initio calculations, reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The SrF 2 films are composed of crystallites with their [1 1 1] direction parallel to the substrate normal, thereby reproducing the symmetry of the substrate. Twinned domains are also observed. At the Ag/SrF 2 interface, fluoride molecules do not dissociate and the interaction with the substrate is weak. At room temperature, fluoride crystallites merge together, resulting in a continuous film covering the entire substrate when it reaches a nominal thickness of 5 nm. Growth at higher temperature induces the formation of triangular 3D islands, leaving sizable portions of the Ag substrate uncovered. At 400 °C, also a small fraction of SrF 2 (0 0 1)-oriented crystallites are observed, with their [1 −1 0] axis rotated by about 30° with respect to the [1 −1 0] substrate direction. [ABSTRACT FROM AUTHOR]

Abstract Given the increasing trend in bacterial antibiotic resistance, research on antimicrobial peptides and their mechanisms of action has become of huge relevance in the last years. Several studies have investigated the effects of a large variety of antimicrobial peptides directly on bacteria or on model lipid bilayers. In the case of model lipid bilayers, different systems are typically exploited; however, different results could be obtained due to the specific properties of the used system. Supported Lipid Bilayers and Giant Unilamellar Vesicles are among the most popular model systems. Here we used Atomic Force Microscopy and fluorescence microscopy to study the interaction of the antimicrobial peptide Magainin H2, an analog of Magainin 2 with increased hydrophobicity, on Supported Lipid Bilayers. We found that, for this kind of model bilayer, due to its strong interaction with the support, the lateral expansion of the membrane induced by the interaction with the peptides is initially inhibited and subsequently proceeds creating new bilayer regions with many defects. This scenario gives rise in Supported Lipid Bilayers to effects like initial increase of lateral pressure, formation of lipid tubes to release this increase, or development of bilayer regions with lower lipid density. Our results highlight that care should be given to the selected model system when studying and comparing the interaction of peptides with other lipid bilayer model systems. Graphical abstract Unlabelled Image Highlights • Different model systems of lipid bilayers interact differently with Magainin H2. • Magainin H2 interacting with Supported Lipid Bilayer could produce lipid tubes. • At low concentration Magainin H2 produces an increase of the lateral tension in Supported Lipid Bilayers. [ABSTRACT FROM AUTHOR]

The piezoelectric response of ZnO thin films in heterostructure-based devices is strictly related to their structure and morphology. We optimize the fabrication of piezoelectric ZnO to reduce its surface roughness, improving the crystalline quality, taking into consideration the role of the metal electrode underneath. The role of thermal treatments, as well as sputtering gas composition, is investigated by means of atomic force microscopy and x-ray diffraction. The results show an optimal reduction in surface roughness and at the same time a good crystalline quality when 75% O2 is introduced in the sputtering gas and deposition is performed between room temperature and 573 K. Subsequent annealing at 773 K further improves the film quality. The introduction of Ti or Pt as bottom electrode maintains a good surface and crystalline quality. By means of piezoelectric force microscope, we prove a piezoelectric response of the film in accordance with the literature, in spite of the low ZnO thickness and the reduced grain size, with a unipolar orientation and homogenous displacement when deposited on Ti electrode. [ABSTRACT FROM AUTHOR]

Atomic force microscopy is an extremely versatile technique, featuring atomic-scale imaging resolution, and also offering the possibility to probe interaction forces down to few pN. Recently, this technique has been specialized to study the interaction between single living cells, one on the substrate, and a second being adhered on the cantilever. Cell–cell force spectroscopy offers a unique tool to investigate in fine detail intra-cellular interactions, and it holds great promise to elucidate elusive phenomena in physiology and pathology. Here we present a systematic study of the effect of the main measurement parameters on cell–cell curves, showing the importance of controlling the experimental conditions. Moreover, a simple theoretical interpretation is proposed, based on the number of contacts formed between the two interacting cells. The results show that single cell–cell force spectroscopy experiments carry a wealth of information that can be exploited to understand the inner dynamics of the interaction of living cells at the molecular level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strontium fluoride forms weakly-interacting interfaces with HOPG. • Dendritic 3D islands which nucleate principally at HOPG steps develop when growth is carried out at room temperature. • A valence band offset of 7 eV between HOPG and SrF 2 is obtained. • High temperature growth causes the formation of almost 1D fluoride nanowires. This study explores the molecular beam epitaxy (MBE) growth of SrF 2 on highly oriented pyrolytic graphite (HOPG) highlighting the temperature-dependent variations in growth morphology, crystalline structure and electronic properties. The comprehensive characterization of SrF 2 /HOPG interfaces was carried out using atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The spectroscopy data suggest that the chemical interaction of the fluoride with the substrate is weak at each deposited thickness and temperature of the substrate during the deposition, indicating a growth under a van der Waals epitaxial regime. SrF 2 nanostructures deposited on HOPG depict a distinctive bulk-like character, concerning their crystallinity and composition, even at the very initial growth stage. Remarkably, temperature plays a crucial role in driving the growth patterns, moving from coalescence of dendritic islands at room temperature to induce nearly 1D rows along the step-edges of HOPG terraces at higher temperatures (400 °C). [ABSTRACT FROM AUTHOR]